Oxide-trapped Charge Densities Research Articles

Effect and Determination of Oxide Trapped Charge and Interface Trapped Charge Density of Threshold Voltage Shift in Irradiated MOSFET by Subthreshold Methodology

This paper presents the effects and determination of oxide and interface trapped charge density of threshold voltage shift in irradiated MOSFET by subthreshold methodology. The designed dimension, channel width per channel length (W/L) is 20 µm/20 µm. The threshold voltage is extracted by a linear extrapolation methodology. The over all threshold voltage shifts are caused by oxide trapped charge and interface trapped charge. The subthreshold methodology determines the interface trapped charge. The 60Co gamma-ray source was used for irradiation to a total dose of 10 kGy. The results showed that the threshold voltage shift is approximately -24 mV/kGy for NMOS and -27 mV/kGy for PMOS. The subthreshold swing shift is approximately 1.2 mV/dec.kGy for NMOS and 0.9 mV/dec.kGy for PMOS. The oxide trapped charge density NOT and interface trapped charge density NIT are found to be increased in NMOS and PMOS respectively. The ratio of ΔNOT/ΔNIT was approximately 2.2 times for NMOS and 2.8 times. Due to the structure, the channel of NMOS is a surface channel whereas the channel of PMOS is a buried channel. Finally, the effect of gamma irradiation on the PMOS was greater than the effect on NMOS observed from the change in threshold voltage and the ratio of ΔNOT/ΔNIT.

Curing defects in plasma-enhanced atomic layer deposition of Al2O3 by six methods

In this paper, the Al2O3 film was fabricated by plasma-enhanced ALD (PEALD) using trimethylaluminium (TMA, Al(CH3)3) precursor. For curing defects such as hydroxyl (OH), Hydrogen, and Carbon inside Al2O3, six types of treatments combining rapid thermal annealing (RTA) or H2 plasma were applied. The comprehensive electrical characteristics such as C-VG, flat-band voltage (Vfb) were quantitatively analyzed by comparing interface trap density (Dit), oxide trapped charge density (Not), permittivity, and breakdown field. RTA is crucial to reduce Dit, Not by ∼78.2% and ∼86.7%, respectively, and enhance the breakdown field from 9 MV/cm to 14 MV/cm or higher by forming the interfacial layer. However, it was not adequate to prevent the severe Vfb shift and decrease of permittivity. H2 plasma pre-treatment could be a solution for these problems as well as slightly improve the breakdown property. But the widening of Vfb variation was still concerned because the amount of carbon reduced by H2 plasma treatment is not consistent. Thus, a more precise H2 plasma treatment is necessary for reliable threshold voltage distribution.

Effect of high-radiation-dose-induced structural modifications of HfSiO4/n-Si on electrical characteristics

High-k/n-Si structures were formed with HfSiO4 films annealed at the temperature range of RT (room temperature)-900 °C and radiation-induced structural modifications were determined by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) techniques in the study. The effect of oxygen-deficient bond contents on the electrical characteristics of HfSiO4 pMOS (n type Metal Oxide Semiconductor) capacitors whose radiation response was investigated in the 0–50 kGy dose range was investigated. While no XRD peak was observed before and after irradiation at RT and 500 °C-HfSiO4/n-Si, crystallization started with irradiation at 900 °C. The dielectric constant of the film was found in the range of 16–23. It was determined that Hf–Hf oxygen-deficient bonds act as negative charge trapping centers, while Hf–Si and Si–Si oxygen-defective bonds act as positive charge trapping centers. The direction of the C–V (Capacitance-Voltage) curve changed continuously with increasing radiation dose. The change in the interface trap charge density was found to be higher than the change in the oxide trap charge density for all doses in RT-HfSiO4 pMOS capacitor and for 1 kGy at 500 °C-HfSiO4 pMOS capacitor. Oxygen defective bond content and Hf-O-Si/Si–O–Si ratios were sufficient to establish a link between structural analyses and electrical characteristics at some doses. In some cases, the frequency-dependent charges had a more dominant effect on the radiation response of the device compared to the oxide trap charges.

Effect of deposition temperature and surface reactions in atomic layer deposition of silicon oxide using Bis(diethylamino)silane and ozone

We investigated the effect of deposition temperature on the properties of the silicon oxide films produced by alternating exposures to bis(diethylamino)silane (BDEAS) and ozone (O3). The surface reactions during the deposition were studied using in situ characterization techniques and density functional theory (DFT) calculations. The atomic layer deposition (ALD) temperature window was between 250 and 350 °C with a nearly constant growth rate of ∼ 0.10 nm/cycle and the step coverage higher than 94%. The saturation doses of BDEAS and O3/O2 were 5 × 106 L and 5 × 107 L. Among the films deposited in genuine ALD mode, the film deposited at 350 °C exhibited the lowest leakage current of 2.4 × 10-8 A/cm2 at −2 MV/cm and the lowest oxide trapped charge density of 6.5 × 1011/cm2. The in situ quartz crystal microbalance analysis showed that approximately 0.5 diethylamine ligand per BDEAS molecule was expected to remain on the surface after the BDEAS feeding. The in situ Fourier-transform infrared difference spectrum confirmed the presence of the ligand on the surface. DFT simulations showed that all NEt2 ligands are released on vicinal and geminal hydroxyl groups to form –SiH2*. However, only one NEt2 ligand can be removed on isolated hydroxyls because no other hydroxyls are nearby, resulting in –SiH2(NEt2)*.

Electrical and Optical Characteristics of WOx, ZrHfO, and Tri-Layer WOx Embedded ZrHfO High-k Based SSI-LEDs

The solid state incandescent light emission device (SSI-LED), which can emit the broadband warm white light, is made from the high-k MOS capacitor after the dielectric breakdown [1-4]. Electrical properties of the capacitor, such as interface defect density (Dit ), oxide trapped charge density (Qot ), equivalent oxide thickness (EOT), and leakage current density (Jleakage ) are important to the dielectric breakdown process and eventually the optical properties of the emitted light. Since the zirconium hafnium oxide (ZrHfO) high-k material has superb gate dielectric properties, e.g., high crystallization temperature, low interface state density, oxide trapped charges, and high effective k value, it has been used as the gate dielectric layer of the MOS capacitor [5,6]. On the other hand, the WOx dielectric-based MOS capacitor and SSI-LED has been studied. The latter emitted light with relative high intensity due to the high emissivity coefficient of the W component [7]. However, the capacitor has a high leakage current which can be a reliability concern. In this paper, three types of MOS capacitors, i.e., with gate dielectrics made of ZrHfO, WOx, and ZrHfO/WOx/ZrHfO/WOx/ ZrHfO/WOx/ZrHfO, separately, have been fabricated into SSI-LEDs and studied for electrical and optical properties.MOS capacitors were prepared on a DHF pre-cleaned p-type <100> silicon (1015 cm-3) wafer. For the ZrHfO capacitor, the gate dielectric layer was sputter-deposited from the Zr/Hf (12/88 wt%) target in Ar/O2 (100:100 sccm) at 5 mTorr and 60 W for 12 min. The WOx layer was sputter-deposited from the W target (99.999 %) in Ar/O2 (40:100 sccm) at 5 mTorr and 60 W for 12 min. For the WOx embedded capacitor, the ZrHfO (2 min)/WOx (2 min)/ZrHfO (2 min)/WOx (2 min)/ ZrHfO (2 min)/WOx (2 min)/ZrHfO (2 min) stack was deposited in one pump down under the same conditions as each individual layer. The post-deposition annealing (PDA) was conducted at 900 ̊C under the O2 atmosphere for 5 min in furnace. An 80 nm thick ITO was sputter deposited and wet etched into round gate electrodes using an aqua regia solution. Then, the backside of the wafer was deposited with an aluminum thin film and annealed at 400 ̊C under H2/N2 (10/90) for 5 min. The dielectric breakdown voltage of the capacitor was determined from the current density-gate voltage (J-V) curve. The light emission characteristics the SSI-LED were measured from an optical emission spectrometer (OES, StellarNet).Electrical characteristics of the capacitors before and after the dielectric breakdown were discussed with respect to the gate dielectric material properties. Figure 1 shows the emission spectra of the 3 SSI-LEDs. They all emit broad band light in the range of UV to near IR. They are similar to the visible wavelength region of the solar light. The peak lengths λpeak’s of the ZrHfO, WOx, and WOx embedded devices are 638 nm, 687.15 nm, and 663 nm, respectively. The WOx SSI-LED has the highest emission intensity. It was reported that the emissivities of the pure (99.99 %) tungsten and the hafnium-3 wt% zirconium materials were 0.434 [8] and 0.30 [9] at 2000 K, respectively. Therefore, the inclusion of W component in conductive path may increase the light emission intensity of SSI-LED. According to the emission spectra, the CIE chromaticity chart has been prepared. The color correlation temperatures (CCT’s) and color rendering indices (CRI’s) were calculated. Y. Kuo, ECS Trans., 69, 23-29 (2015).C.-C. Lin and Y. Kuo, ECS J. Solid State Sci. Technol., 3, Q182 (2014).C.-C. Lin and Y. Kuo, J. Vac. Sci. Technol. B, 32, 011208 (2014).Y. Kuo and C.-C. Lin, Appl. Phys. Lett., 102, 031117 (2013).T.-C. Chang, F.-Y. Jian, S.-C. Chen and Y.-T. Tsai, Materials today, 14, 608-615 (2011).G. E. Moore, Cramming more components onto integrated circuits, McGraw-Hill New York, NY, USA (1965).M. Lorenz, H. von Wenckstern and M. Grundmann, Adv. Mater., 23, 5383-5386 (2011).R. D. Larrabee, JOSA, 49, 619-625 (1959).P.-F. Paradis, T. Ishikawa and S. Yoda, Int. J. Thermophys., 24, 239-258 (2003). Figure 1

(G03 Best Paper Award Winner) Si-Passivated Ge Gate Sacks with Low Interface State and Oxide Trap Densities Using Thulium Silicate

Germanium is considered as a high mobility channel material for its potential to be introduced in future CMOS technology nodes. Ge surface passivation with a thin silicon layer (Si-cap) has been shown to be efficient for pFETs because of a sufficient valence band offset between Ge and Si-cap, which confines the holes in the Ge layer. Strained Ge pFinFETs outperforming Si pFinFETs due to four times higher mobility have been demonstrated using Si-cap process [1]. Interfacial defects can be further passivated with a high-pressure anneal in H2 resulting in reduced sub-threshold swing and increased mobility in Ge nanowires [2]. Moreover, by using a Si-cap, Negative-bias temperature instability reliability is improved compared to GeOx passivation because of the energy decoupling between holes and defects in SiO2/HfO2 gate stack [3]. However, a Si-cap process poses gate stack scalability issues because in order to achieve sufficient surface passivation, the Si-cap thickness cannot be scaled. An introduction of a high-k interfacial layer instead of a chemical oxide SiO2 could potentially help to scale down equivalent oxide thickness. Integrating thulium silicate (TmSiO) as a replacement of the SiO2 interfacial layer has been demonstrated on silicon, and a hole and electron mobility enhancement compared to SiO2/HfO2 gate stacks has been achieved for an equivalent oxide thickness (EOT) < 1 nm [4]. Moreover, we have previously displayed the compatibility of Tm2O3 with Ge by demonstrating GeOx/Tm2O3 gate stacks with interface state density Dit < 5·1011 eV-1cm-2 [5]. In this work, we integrate TmSiO with a Si-cap process to achieve Dit comparable to GeO2 passivation.In order to evaluate Ge/Si/TmSiO interfaces, MOS capacitors (MOSCAPs) were fabricated on n-type Ge strain relaxed buffers epitaxially grown on n-type Si wafers in a two-step process using GeH4 precursor [6]. Si-caps of different thicknesses were grown at 400 °C using Si2H6. Si growth was confirmed by ellipsometry spectroscopy and testing that the surface is hydrophobic. While trying to keep the Si-cap exposure to air to a minimum, 400 nm PECVD SiO2 was deposited and active areas were defined. After removing the remaining SiO2 from the active areas with 1 % HF, Tm2O3 was deposited by atomic layer deposition (ALD) at 225 °C. Rapid thermal anneal at 550 °C for 60 s in N2 was then employed to form TmSiO layer. High-k HfO2 was deposited by ALD at 350 °C followed by a post deposition anneal in O3 for 10 min. TiN gate metal was deposited at 425 °C by ALD and 500 nm Al was deposited by sputtering for probing purposes. After patterning, the samples were subjected to a forming gas anneal of 10% H2 in N2 at 400 °C for 30 min. Reference MOSCAPs with Ge/GeOx/Tm2O3/HfO2 gate stacks were also fabricated as described in [5] with addition of ALD HfO2.Interface state density in the midgap of Ge/Si/TmSiO/Tm2O3/HfO2 gate stacks was evaluated by CV measurements where measured CV characteristics where compared to calculated ones assuming a parabolic Dit distribution. Dit highly depends on Si-cap thickness, as displayed in Fig. 1. An optimal Si-cap thickness corresponding to 40-50 min deposition time provides Dit at midgap ~5·1011 cm-2eV-1 at CET of 4 nm. Reference MOSCAPs with Ge/GeOx/Tm2O3/HfO2 gates exhibit similar Dit of 4-5·1011 cm-2eV-1. Interface state density distribution within the band gap of Ge/Si/TmSiO interface with 40 min Si-cap deposition time was evaluated using the conductance method at different temperatures and is displayed in Fig. 2. Dit in the midgap is in agreement with the results obtained from CV measurements, and increases towards the valence and conduction band edges. The oxide trapped charge Qox of 2.5·1010 cm-2 (40 times lower than in the Ge reference devices without Si-cap) was determined from CV measurements and corresponds to only 5 mV hysteresis showing the potential of superior reliability.A Si-cap process with high-k TmSiO interface has been demonstrated on Ge MOS devices. A low Dit comparable to GeOx passivation has been shown. In addition, devices with TmSiO potentially have a superior reliability vs GeOx devices due to low oxide trapped charge density.

Influence of frequency and gamma irradiation on the electrical characteristics of Er2O3, Gd2O3, Yb2O3, and HfO2 MOS-based devices

The unique physical, chemical, and electronic properties of rare earth oxides have been of immense interest to replace SiO2 as a dielectric material in metal–oxide–semiconductor (MOS)-based sensors applications to accurately measure the radiation dosage and increase sensor sensitivities in as diverse applications as space radiation, nuclear physics, medical diagnostics, radiation cancer therapy, and personal dosimetry devices. Hence, the electrical characteristics of oxides prior to and after irradiation of MOS-based devices are needed since they are the backbone of the devices such as MOSFETs and ICs. In addition, an understanding of the behaviour of high-k dielectric oxides in an MOS configuration is necessary since the radiation-induced damage occurs in the bulk oxide film and/or near the oxide–semiconductor interface resulting in creation of lattice defects. Hence, MOS structures with the rare earth oxides of Er2O3, Gd2O3, Yb2O3, and a transition metal oxide of HfO2 were produced by RF magnetron sputtering to determine (a) the structure of the films, (b) dielectric constants, (c) capacitance versus voltage behaviour of Er2O3, Gd2O3, Yb2O3, and HfO2 prior to and after irradiation of the devices in the dose range of 0–76 Gy. The experimental results were analysed with a theoretical framework on the energy band diagram and the radiation effects on the electrical characteristics of the MOS capacitors. The characteristics of the devices were evaluated by using effective oxide charge density ( $$ Q_{\text{EFF}} $$ ), variation in the oxide trapped charge density ( $$ \Delta N_{\text{ox}} $$ ), and interface trapped charge density ( $$ \Delta N_{\text{it}} $$ ). In addition, barrier height ( $$ \phi_{\text{b}} $$ ), image force barrier lowering ( $$ \Delta \phi_{\text{b}} $$ ), acceptor concentration ( $$ N_{\text{a}} $$ ) were calculated before and after irradiation and examined the nature of interface states. The radiation responses of the Er2O3 and HfO2 MOS capacitors did not show a stable behaviour with an increase in radiation dose due to possible neutral electron trap centres. Contrary to expectations, we infer that more negative charges are trapped in Gd2O3-based device than positive charges with an increase in radiation dose. The C–V curves of the Yb2O3 MOS capacitor shifted in the same direction at both 100 kHz and 1 MHz, and as expected, positive charge traps in the structure are more efficient than negative charges. The observed sensitivities of Yb2O3 MOS capacitors are 4–7 times higher than those of SiO2, and the sensitivities of the Yb2O3 MOS capacitors with a total radiation dose of 70 Gy were found to be around 28.08 mV/Gy at both 100 kHZ and 1 MHz frequencies. The Yb2O3 appears to be a promising dielectric candidate for developing a new generation of radiation sensors with an excellent interface quality when compared to rare earth mixed oxides such as silicates, transition metal oxides, and the silicates based on transition metals, Al2O3, and BiFeO3. Our review of the literature suggests that while the radiation damage has been assessed comprehensively based on the C–V characteristics, microstructural characterization of the irradiated films and their interfaces is lacking even though the quality of oxide/Si interface is the most important feature of the devices. The electrical data should be correlated with the inferences from XPS, AFM, TEM, XRD, and other techniques. Further progress requires selection and validation of material properties based on theoretical calculations and predications, utilization of diverse thin film processing and characterization techniques, determining the effect of thickness on the properties of MOS capacitors, a thorough understanding of the interfaces, effect of frequency on the MOS capacitors and the interface characteristics, effect of radiation on the physical, interfacial, and electrical characteristics of MOS capacitors, and preparation and characterization of sensors based on thin films of novel mixed oxides and silicates of different chemistries.

Investigation of band alignment between InAlAs and atomic-layer-deposited HfO2/Al2O3 by X-ray photoelectron spectroscopy

Band alignments between atomic layer deposition (ALD) HfO2/Al2O3 double layers and InAlAs were investigated by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The relationship of As and Hf 4f peaks reducing with the decreasing take-off angle θ indicated upward band bending on the InAlAs surface and a potential gradient in the HfO2/Al2O3 layer. AR-XPS measurements were combined with numerical calculations. The valence band and conduction band discontinuity between HfO2/Al2O3 and InAlAs were 2.49 ± 0.2 eV and 1.86 ± 0.2 eV, respectively. A low leakage current density of 7.01 × 10−7 A cm−2 at 1 V and oxide trapped charge densities of 9.925 × 1011 cm−2 were obtained.

Modulation of the interfacial and electrical properties of atomic-layer-deposited Hf0.5Al0.5O/Si gate stacks using Al2O3 passivation layer with various thickness

The interfacial properties and electrical characteristics of atomic layer deposited Hf0.5Al0.5O/Si with different Al2O3 barrier layer thicknesses have been investigated. X-ray photoelectron spectroscopy measurements have shown that a 1-nm-thick Al2O3 buffer layer can effectively suppress the silicate formation and improve interfacial properties. Accordingly, the sample with a 1-nm-thick Al2O3 layer exhibits improved electrical properties, including the lowest density of oxide charge of 3.16 × 1010 cm−2, an interface charge density of 0.82 × 1011 cm−2 eV−1, and an oxide trapped charge density of 0.79 × 1011 cm−2. The reduced leakage current at an applied substrate voltage of 1 V is 3.28 × 10−6 A/cm2. Furthermore, the carrier transportation mechanism of Al/Hf0.5Al0.5O/Al2O3/Si/Al MOS device has been researched systematically. Through the analysis, it could be found that for all samples, thermionic emission and Poole–Frenkel emission are dominant mechanisms of carrier transport under a low electric field region, as well as Fowler–Nordheim tunneling is the main carrier transport mechanism at a high electric field region.

A comprehensive study on usage of Gd2O3 dielectric in MOS based radiation sensors considering frequency dependent radiation response

The purpose of this study is to investigate the Gadolinium Oxide (Gd2O3) as a gate dielectric/sensitive region in MOS based radiation sensors and to provide a detailed description of the frequency-dependent gamma irradiation response of a Gd2O3 MOS capacitor. The 254 nm thick-Gd2O3 films were deposited on p-type Si wafers by using RF magnetron sputtering. The radiation response of the Gd2O3 MOS capacitors was investigated by 60Co irradiation in the range of 0.5–70 Gy. The capacitance-voltage (C-V) curves shifted to a more positive potential with increasing radiation dose due to there being more trapped electrons than holes. The variation in the oxide trap charge density was found to be in the range of − 3.21 × 1011 ± 1.57 × 1010 cm−2 – − 1.70 × 1012 ± 8.33 × 1010 cm−2 at 100 kHz and − 2.26 × 1011 ± 1.02 × 1010 cm−2 – − 1.30 × 1012 ± 6.02 × 1010 cm−2 (70 Gy) at 1 MHz. The maximum variation in the interface trap charge density was in order of 1011 cm−2 at 1 MHz. The results indicate that the contribution of the oxide trap charge to radiation response of the Gd2O3 MOS capacitor is higher than that of the interface trap charges. The radiation sensitivities of the Gd2O3 MOS capacitor for 100 kHz and 1 MHz were determined as 59.2 ± 2.9 mV/Gy and 62.7 ± 2.9 mV/Gy, respectively. The percentage fading values (dose storage capability) measured in the time range of 25–145 min for 100 kHz varied from 2.2% to 11.4%.

Analysis of the electrical properties and current transportation mechanism of a metal oxide semiconductor (MOS) capacitor based on HfGdO gate dielectrics

The microstructure, optical and electrical properties of sputtering-derived HfGdO high-k gate dielectric thin films as a function of the Gd doping content have been systematically investigated. X-ray diffraction (XRD) measurements have indicated that Gd doping can form a new stable cubic phase. The optical band gap of the HfGdO gate dielectrics increases gradually from 5.82 to 6.14 eV as the Gd doping concentration increases. The electrical properties, such as permittivity, oxide trapped charge density, border trap charge density and leakage current density of samples, are determined using a semiconductor device analyzer. The formation mechanism of leakage current is also discussed in detail. In addition, the interfacial properties of HfGdO/Si gate satcks were tested to establish the electrical properties. The excellent optoelectronic properties, such as the optical band gap of 5.95 eV, leakage current density of 8.33 × 10−8 A/cm2 at a bias voltage of 2 V, oxide trapped charge density of −1.06 × 1012 cm−2 and a border trap charge density of zero and optimized interfacial properties were observed in the HfGdO thin films with sputtering power of 30 W, indicating that it may become a potential high-k gate dielectric in future complementary metal oxide semiconductor (CMOS) devices.

Proposal of alternative sensitive region for MOS based radiation sensors: Yb2O3

The purpose of this study is to investigate the usability of ytterbium oxide (Yb2O3) as a sensitive region/gate oxide in metal oxide semiconductor (MOS) based dosimeters and to determine the advantages and disadvantages of this device relative to its alternatives. For this purpose, amorphous Yb2O3 films were grown on p type Si by radio-frequency magnetron sputtering and aluminum (Al) was used as front and back ohmic contacts of the capacitor. Yb2O3 MOS devices were irradiated incrementally to the total dose of 70 Gy by 60Co radioactive source. The capacitance–voltage measurements were performed at low (100 kHz) and high (1 MHz) frequencies to examine the behavior of the traps. The sensitivity of the device for 70 Gy was obtained using flat band voltage shifts as 27.5 ± 1.1 and 28.1 ± 1.3 mV/Gy for 100 kHz and 1 MHz, respectively. The changes in the oxide trap charge densities in the studied dose between 0.5 and 70 Gy are in the ranges of (1.09 ± 0.04)× 1011–(1.23 ± 0.05) × 1012 cm−2 for 100 kHz and (−3.26 ± 0.08) × 1010–(8.16 ± 0.35) × 1011 cm−2 for 1 MHz. For both frequencies, there was no significant change in the interface trap charge densities over the applied dose and the density of these traps remained in order of 1011 cm−2 after each applied dose. The percentage fading were measured at only 1 MHz for evaluation of the device's dose storage capacity and the results varied from 4% (5 min) to −19% (50 min). An almost constant fading value was obtained after 20 min from irradiation. The capacitor's sensitivity was found to be higher than those of similar devices composed of HfO2, La2O3, SiO2, Sm2O3, and Y2O3. Yb2O3 would be a promising candidate for a new generation of MOS based radiation sensors.

Study of Bias-Temperature Instability in HfO2 sputtered Thin Films by Post Nitrogen Annealing for the Advanced CMOS Technology

This paper presents a study on Negative bias temperature instability (NBTI) on high-k HfO2 sputtered thin films annealed in oxygen and nitrogen ambient. Activation energies for interface, oxide-trap charge and switching states densities for each oxygen and nitrogen ambient annealed devices is estimated from capacitance-voltage measurements versus temperature characteristics. It is found in the range 0.13eV-0.16eV for oxygen annealed sample and 0.47eV – 0.7eV for nitrogen annealed sample. Nitrogen annealed sample shows higher activation energy and low traps charge densities.

Evaluation of Radiation Sensor Aspects of $\text{Er}_2$$\text{O}_3$ MOS Capacitors under Zero Gate Bias

The aim of the present study is to investigate the usage of Erbium Oxide ( $\text {Er}_2$ $\text {O}_3$ ) as a gate dielectric in MOS-based radiation sensors. $\text {Er}_2$ $\text {O}_3$ thin films were deposited on a p-type Si (100) substrate via RF magnetron sputtering and were annealed at 500° C under $\text {N}_2$ ambient. The structural properties of the $\text {Er}_2$ $\text {O}_3$ thin films were determined via XRD, FTIR, and AFM analyses. The Erbium silicate formation was not observed in the XRD and FTIR spectra. The roughness root-mean-square was measured as 16.4 nm by the AFM analysis. Following the description of the film, the $\text {Er}_2$ $\text {O}_3$ MOS capacitors were fabricated and irradiated by a $^{60}\hbox{Co}$ radioactive source in different doses varying from 4 Gy to 76 Gy. The capacitance–voltage (C-V) curves shifted to the right side compared to the ideal one in the dose range of 4–16 Gy and to the left side from 16 Gy to 76 Gy. The oxide trapped charge density increased with an increasing irradiation dose. A significant variation in the interface states densities was not observed, the value of which always remained in the order of $10^{10} $ $\text {eV cm}^{-2}$ in the studied dose range. Based on these results, it can be said that gamma radiation does not cause a significant deterioration during irradiation. The calibration curve of the capacitor was obtained from the flat band voltage shifts depending on the gamma dose. Some electrical parameters, such as the barrier height and acceptor concentration, were investigated depending on the gamma dose. The sensitivity of the capacitor was determined to be 107 mV/Gy for the dose range of 4–16 Gy and 61 mV/Gy for the dose range of 16–76. These results showed that the $\text {Er}_2$ $\text {O}_3$ MOS capacitor was more sensitive to the gamma radiation compared to the $\text {SiO}_{2}$ and $\text {Sm}_2$ $\text {O}_3$ -based capacitors.

Quantitative separation of radiation induced charges for NPN bipolar junction transistors based on 1/f noise model

Ionizing-radiation-induced oxide-trapped charges and interface states cause the current and 1/f noise degradation in bipolar junction transistors. In order to better understand these two degradation mechanisms and develop hardening approaches for a specific process technology, it is necessary to measure the effect of each mechanism separately. In recent years, several techniques have been developed, but no charge-separation approach based on 1/f noise for NPN bipolar junction transistors is available. In this paper, the effects of ionizing-radiation-induced oxide trapped charges and interface states on base current and 1/f noise in NPN bipolar junction transistors are studied in detail. Firstly, a new model of base surface current of NPN bipolar junction transistors is presented with some approximations, based on an available model for the base surface current under certain conditions; this model can identify the physical mechanism responsible for the current degradation. Secondly, combining the theory of carrier number fluctuation and the new model of base surface current another model is developed which can well explain the 1/f noise degradation. This model suggests that the induced oxide-trapped charges would make more carriers, involving the dynamic trapping-detrapping, which leads to the 1/f noise to increase; and the induced oxide-trapped charges and interface states can also bring about an increase in base surface current which can also cause the l/f noise increase. These two models suggest that the current and1/f noise degradations can be attributed to the same physical origin, and these two kinds of degradations are the result of accumulation of oxide-trapped charges and interface states. According to these two models, simple approaches for quantifying the effects of oxide-trapped charges and interface states are proposed. The base surface current can be extracted from the base current using the available method. The oxide-trapped charge density is estimated using the amplitude of 1/f noise (10-100 Hz) and the base surface current. Given the estimated oxide-trapped charge density, the interface state density can be estimated using the base surface current. These methods are simple to implement and can provide insight into the mechanisms and magnitudes of the radiation-induced damage in NPN bipolar junction transistors.

Ni/CNT/SiO2 구조의 4H-SiC MIS 캐패시터의 전기적 특성

본 연구에서는, Ni/CNT/<TEX>$SiO_2$</TEX> 구조의 4H-SiC MIS 캐패시터를 제작하고 전기적 특성을 조사하였다. 이를 통하여 4H-SiC MIS 소자에서 탄소나노튜브의 역할을 분석하고자 하였다. 탄소나노튜브는 이소프로필알코올과 혼합하여 <TEX>$SiO_2$</TEX> 표면에 분산하였다. 소자의 전기적 특성 분석을 위하여 300-500K의 온도 범위에서 소자의 정전용량-전압 특성을 측정하였다. 밴드 평탄화 전압은 양의 방향으로 shift되었다. 정전용량-전압 그래프로부터 계면 포획 전하 밀도 및 산화막 포획 전하 밀도가 유도되었다. 산화막의 상태는 4H-SiC MIS 구조의 계면에서 전하 반송자 또는 결함 상태와 관련된다. 온도가 증가함에 따라 밴드 평탄화 전압은 음의 방향으로 shift되는 결과를 얻었다. 실험 결과로부터, Ni과 <TEX>$SiO_2$</TEX> 계면에 탄소나노튜브를 첨가함에 따라 4H-SiC MIS 캐패시터의 게이트 특성을 조절 가능할 것으로 판단된다. In this study, the electrical characteristics of Ni/CNT/<TEX>$SiO_2$</TEX> structures were investigated in order to analyze the mechanism of carbon nanotubes in 4H-SiC MIS device structures. We fabricated 4H-SiC MIS capacitors with or without carbon nanotubes. Carbon nanotubes were dispersed by isopropyl alcohol. The capacitance-voltage (C-V) is characterized at 300 to 500K. The experimental flat-band voltage (<TEX>$V_{FB}$</TEX>) shift was positive. Near-interface trapped charge density and oxide trapped charge density values of Ni/CNT/<TEX>$SiO_2$</TEX> structure were less than values of reference samples. With increasing temperature, the flat-band voltage was negative. It has been found that its oxide quality is related to charge carriers or defect states in the interface of 4H-SiC MIS capacitors. Gate characteristics of 4H-SiC MIS capacitors can be controlled by carbon nanotubes between Ni and <TEX>$SiO_2$</TEX>.

탄소나노튜브를 첨가한 4H-SiC MOS 캐패시터의 전기적 특성

In this study, the electrical characteristics of the nickel (Ni)/carbon nanotube (CNT)/<TEX>$SiO_2$</TEX> structures were investigated in order to analyze the mechanism of CNT in MOS device structures. We fabricated 4H-SiC MOS capacitors with or without CNTs. CNT was dispersed by isopropyl alcohol. The capacitance-voltage (C-V) and current-voltage (I-V) are characterized. Both devices were measured by Keithley 4200 SCS. The experimental flatband voltage (<TEX>$V_{FB}$</TEX>) shift was positive. Near-interface trap charge density (<TEX>$N_{it}$</TEX>) and negative oxide trap charge density (<TEX>$N_{ox}$</TEX>) value of CNT embedded MOS capacitors was less than that values of reference samples. Also, the leakage current of CNT embedded MOS capacitors is higher than reference samples. It has been found that its oxide quality is related to charge carriers and/or defect states in the interface of MOS capacitors.

The impact of stress-induced defects on MOS electrostatics and short-channel effects

This paper investigates the influence of stress-induced oxide-trapped charge and interface traps on the electrostatics of metal–oxide–semiconductor (MOS) devices and its relation to short-channel effects (SCE). Interface trap and oxide-trapped charge densities are included in the derivation of scaling models that are based on solving Poisson’s equation in the depletion approximation (i.e., in weak inversion) using analytical approximations for the electrostatic potential. The impact of interface traps and oxide-trapped charge on the electrostatic potential profile, scaling, and short-channel effects are modeled analytically and verified with TCAD simulations. The theory and modeling approach is validated through comparisons with the experimental extraction of SCE in n-channel MOS field-effect transistors (MOSFETs) measured before and after hot-carrier stress.

Modeling Radiation-Induced Degradation in Top-Gated Epitaxial Graphene Field-Effect-Transistors (FETs)

This paper investigates total ionizing dose (TID) effects in top-gated epitaxial graphene field-effect-transistors (GFETs). Measurements reveal voltage shifts in the current-voltage (I-V) characteristics and degradation of carrier mobility and minimum conductivity, consistent with the buildup of oxide-trapped charges. A semi-empirical approach for modeling radiation-induced degradation in GFETs effective carrier mobility is described in the paper. The modeling approach describes Coulomb and short-range scattering based on calculations of charge and effective vertical field that incorporate radiation-induced oxide trapped charges. The transition from the dominant scattering mechanism is correctly described as a function of effective field and oxide trapped charge density. Comparison with experimental data results in good qualitative agreement when including an empirical component to account for scatterer transparency in the low field regime.

Total-Dose Radiation Response of HfLaO Films Prepared by Plasma Enhanced Atomic Layer Deposition

HfLaO and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films were deposited by plasma enhanced atomic layer deposition (PEALD). PEALD makes in-situ plasma treatment possible, and the film growth temperature can be reduced. The films were characterized. High resolution transmission electron microscopy (HRTEM) indicated both films were amorphous. X-ray photoelectron spectroscopy (XPS) suggested that the interface layer was most likely composed of Hf-Si-O and La-Si-O. MIS capacitors with HfLaO and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectrics were irradiated by gamma rays with the dose up to 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> rad (Si). Electrical measurements indicated that the dielectrics showed relatively stable electrical properties. The equivalent oxide thicknesses (EOT) of HfLaO samples were calculated to be 0.9 nm. At a gate condition of |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fb</sub> | = 1 V, the leakage current densities were 0.02 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . With the increasing of the radiation dose, the maximum oxide trap charge density and interface trap charge density for HfLaO samples were calculated to be 2.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and 1.2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , respectively. The analysis of the IV curves suggested that the conduction mechanism in HfLaO samples is the Poole-Frenkel emission.